Automatic cardioverting circuit

ABSTRACT

Pulse generating apparatus which provides electrical heartstimulating pulses only in the absence of normal heart activity. If the patient&#39;&#39;s heart has developed a life threatening arrhythmic condition the inventive apparatus automatically applies an electrical shock to the heart having sufficient magnitude to restore normal heart activity. The inventive apparatus features a redundant heartbeat sensing system which monitors two dynamic characteristics of heart function, for example, heart contraction and EKG. An electrical heart stimulating pulse is delivered to the patient&#39;&#39;s heart following the elapse of a specified period of time since the sensing of a dynamic characteristic indicative of a normal functional heart. Sensing control is automatically regained following successful heart stimulation, thereby inhibiting the application of further electrical pulses. In the event that the patient&#39;&#39;s heart fails to resume normal heartbeat action, the inventive apparatus will continue delivering intermittant shocks-a lower energy pulse is applied first followed by higher energy pulses.

United States Patent 11 1 Denniston et al.

[ AUTOMATIC CARDIOVERTING CIRCUIT [75] Inventors: Rollin H. Denniston,Minneapolis;

Thomas E. Davis, Forest Lake, both Primary Examiner-William E. KammAttorney, Agent, or Firm--Lew Schwartz; Wayne Sivertson of Minn. T

57 ABS RACE" [73] Assignee: Medtronic, Inc., Minneapolis, Minn. 1

- Pulse generating apparatus which provides electncal Filed: 1972heart-stimulating pulses only in the absence of normal heart activity.If the patients heart has developed a 1. N 2 756 [211 App lifethreatening arrhythmlc condltion the inventive apparatus automaticallyapplies an electrical shock to U.S- Cl. D, R the heart having ufficientmagnitude to restore [51] Int. Cl A6ln 1/36 h t a ti it The inventiveapparatus features a Field Of Search R, A1206 redundant heartbeatsensing system which monitors l23/419 419 P, 206 205 205 two dynamiccharacteristics of heart function, for ex- 338/5 ample, heartcontraction and EKG. An electrical heart stimulating pulse is deliveredto the patients heart fol- [56] 1 Re erences C tfi lowing the elapse ofa specified period of time since UNITED STATES PATENTS the sensing of adynamic characteristic indicative of a 3,716,059 2/1973 Welborn et al.128/419 D normal fuPctional Sensing Control 2 3339704 6/1968 Buchowskiet a] 128/419 D cally regamed followmg successful heart stlmulation,2,976,865 3/1961 Shipley 128/205 D th reby inhlbiting the application offurther electrical 3,323,367 6/1967 Searle 338/5 pulses. 1n the eventthat the patients heart fails to re- ,6 ,95 10/1971 Mirowski 6t 128/419D sume normal heartbeat action, the inventive apparatus Haber P ontinuedelivering intermitmant h0cks a lower 3,638,656 2/1972 Grfamlban 128/419P energy pulse is applied first followed by higher energy 3,680,5448/1972 Shmnlck et a1 128/419 P ulses 3,608,545 9/1971 Novack et al.128/206 F p 1 13 Claims, 8 Drawing Figures 24 l EKG 23 [26 l SENSOR OR?5 WAVE 1 2| GATE CONFORMER l CONTRACTION SENSOR 1 l 13 L L m J J H l4IO SYSTEM DISABLE LL 30 l l CONTROLLER I ALERT 3 l l SYSTEM /32 1 00-00I F CONVERTER 34 3e 1 l QTORAGE P5 RE GULAT OR I [I6 I CAPA C lTOR IINTRAVASCULAR L w ELECTRICAL LEAD 1? PATENTED APR 2 3 I974 SHEET 2 UF 5m OE PATENTEDAFR 2a 1974 SHEET 3 [IF 5 E 3950 2596 w 2- ommPATENTEBAPWIQM SHEET 4 BF 5 oom h. 3 @0258. VllilllllJ 52m AUTOMATICCARDIOVERTING CIRCUIT BACKGROUND OF THE INVENTION During the pastseveral decades, coronary heart discase has come to occupy the firstposition among the causes of death in the developed areas of the world.In the United States, for example, this disease is responsible for overone-half million deaths yearly. And of this number, more than half occursuddenly, outside the hospital, and therefore before the patient is ableto obtain the necessary medical assistance. Although the precise causeof sudden death in coronary heart disease has not yet been entirelyclarified, the available evidence permits the medical field to ascribedeath in the majority of these cases to grave disturbances in cardiacelectrical activity culminating in ventricular fibrillation.

Another frustrating but related problem is the present inability to dealeffectively with lethal and nonlethal arrhythmias outside of a hospitalsetting. Within the hospital environment, however, recent experience hasclearly demonstrated that ventricular fibrillation and its frequentprecursor, ventricular tachycardia, are reversible phenomena when promptcardioversion of the heart is instituted. Under such circumstances,cardiac function can frequently be restored to normal without thepatient suffering from residual disability. Unfortunately, however, thepresent state of the art makes cardioversion very dependent upon ahighly specialized medical environment, thus limiting such treat- ,mentto fully equipped, modern hospitals.

There is no question that a great need exists for a defibrillator whichwould be carried by those who are prone to having one of the manylife-threatening arrhythmias generally discussed above. Thus, in some patients having coronary heart disease,-a fatal outcome from ventriculartachycardia or ventricular fibrillation could be avoided, even in theabsence of immediate medical assistance. The first step, of course, isthe detection of those prone to suffering from cardiac malfunctionsleading to ventricular tachycardia or ventricular fibrillation.

While it is not possible to predict with unerring exactness whichpatients suffering from coronary heart disease will die from ventricularfibrillation or ventricular tachycardia, several high risk groups ofpatients can be recognized. For example patients who have experiencedmyocardial infarction, even though they may be surviving in good'health,runa substantial risk of dying suddenly, a risk several times greaterthan that asso ciated with the general population. Further, if patientswith myocardial infarction have a history of serious ventriculararrhythmias and/or of cardiac arrest, or if evidence of persistentmyocardial irritability is present, it may be logically assumed that therisk of sudden death is increased substantially. A patient like thosedescribed above would greatly benefit from an automatic defibrillator.

Also, such an automatic defibrillator would be an asset to thosepatients who have suffered myocardial infarction in the coronary careunit and remain hospitalized in the coronary care unit or some otherarea of the hospital. Under such circumstances, the defibrillator couldbe used temporarily for the remainder of the expected hospital stay; orthe automatic defibrillator could be permanently implanted for use bothin the hospital and after discharge. And another recognizable class ofpatients particularly in need of an automatic defibrillator is the classcomposed of those who have not shown prior histories of myocardialinfarction but who show severe symptoms of coronary heart disease, suchas ventricular arrhythmias resistant to medical treatment or anginapectoris.

From the brief discussion above, there should be little doubt that thepossible applications for an automatic defibrillator are numerous. Suchan automatic defibrillator has been developed by Medtronic, Inc. and isdescribed in US. Pat. application Ser. No. 124,326, filed Mar. 15, 1971,now abandoned by Mieczyslaw Mirowski, et al. and entitled CARDIOVER- TERHAVING SINGLE INTRAVASCULAR CATHE- TER ELECTRODE SYSTEM.

The automatic standby defibrillator described in the above-identifiedpatent application employs a pressure sensing element attached to a bodyimplantable electrical lead such that it can be positioned within theright ventricle of the heart. Since the pressure in the heart dropsseverely when the heart goes into the fibrillation state, ventricularfibrillation can be easily detected by monitoring heart pressure.However, several difficulties with measuring heart pressure areencountered. One disadvantage with using pressure as an indicator of thefibrillation state is that the small pressure sensing elements which aresuitable for use with body implantable electrical leads are quiteexpensive. A second disadvantage with using these pressure sensingelements is that they must either be located alongside, on the outersurface, or at the tip of the body implantable electrical ened by thesurrounding heart muscle.

The apparatus of this invention uses a single ,intravascularelectrode'of the type described in US. Pat. application Ser. No.202,238, filed Nov. 26, 1971, by Rollin H. Denniston, lll, entitledMUSCLE CONTRAC- TION DETECTION APPARATUS, to perform three functions;namely; (1) detecting heart contractions;

(2) detecting heart electrical activity in the form of R waves; and (3)applying electrical impulses to the heart for cardioverting it.

Thus the apparatus of this invention overcomes many difficultiesexistent in the prior art devices while providing a compact andpractical automatic cardioverting system. i

SUMMARY OF THE INVENTION The present invention relates to acardioverter, an electronic system which, after detecting one of theabove-noted lethal or non-lethal arrhythmias, automatically cardiovertsthe heart of the user. Cardioverting or cardioversion" as used herein isintended to mean a method of correcting a number of arrhythmic heartconditions including atrial tachycardia, atrial fibrillation, junctionalrhythms, ventricular tachycardia, ventricular flutter, and ventricularfibrillation, and any other non-pacing related arrhythmic conditionwhich may be corrected by applying electrical shocks to the heart.Obviously then, defibrillation is included in the term cardioversion asa method of applying electrical shocks to the heart to defibrillate afibrillating atrium or a fibrillating ventricle. The system of thepresent invention may be installed in patients particularly prone todevelop ventricular tachycardia and/or ventricular fibrillation, orother types of tachyarrhythmias which may be corrected by cardioverting,either on a temporary or a permanent basis. And, because of extremelysmall and compact size, the system including both electrodes may betotally and completely implanted under the skin of the patient, oralternatively, may be carried externally, save for the sensing probecarrying the two electrodes.

More particularly, the present invention relates to an automaticcardioverting circuit for monitoring cardiac contraction and sensingwhen the heart has developed an arrhythmic heart condition, and whichthen automatically applies a cardioverting shock to the heart ofsufficient magnitude to restore effective heart rhythm. The device isadapted to continue delivering intermittent shocks to the heart in theevent that the heart fails to return to its normal behavioral pattern,and has the ability of automatically regaining sensing control over afunctional heart, thereby insuring that further shocks are inhibitedafter successful cardioversion has taken place.

The automatic cardioverting circuit comprises two basic subsystems;asensing system, which continuously monitors heart activity; and astimulation system which upon receiving a signal from the sensing systemapplies a cardioverting shock to the heart myocardium through anintravascular electrical lead.

The sensing system of the present invention monitors two dynamiccharacteristics of the heart and provides an electrical signalcorresponding to each heart contraction. The absence of both thesecharacteristics for a predetermined period of time is required beforethe stimulation system will be activated to transmit a cardiovertingshock to the heart. One of the characteristics monitored is the EKG. TheEKG is obtained from the electrodes located on the intravascular lead.The second characteristic monitored is muscle contraction. The musclecontraction signal is obtained from a contraction sensing devicepositioned in the intravascular lead and consisting of a conductiveelastomer body having carbon particles imbedded therein. The contractionsignal is generated whenever the contraction sensing device is flexed bya heart contraction.

The EKG and the heart contraction signals are fed to a gating device.The gating device will allow a cardioverting shock to be delivered tothe heart only if both signals are absent for a predetermined period. oftime. Thus a heart contraction detected by either the EKG monitoringsystem or the heart contraction monitoring system is sufficient toprevent a cardioverting pulse from being delivered to the heart.Consequently, each of the monitoring devices provides a back-up signalfor the other.

The stimulation portion of the present invention ap' plies energy to theheart in the form of electrical pulses delivered through the electrodeslocated on the intravascular lead. The application of these electricalpulses to the patients heart is delayed for a preset period of time (onthe order of -20 seconds) following the sensing of abnormal heartactivity. If normal cardiac action resumes during this period, theapplication of the cardioverting pulses is automatically inhibited. Thisdelay gives the heart the opportunity to convert spontaneously to normalcardiac rhythm if it is able to do so, and also insures that thecardioverting pulses are applied only when they are needed.

The present invention comprising the sensing system and the stimulationsystem provides an automatic cardioverting device capable ofcardioverting a malfunctioning heart at relatively low energy levels.This device senses when the heart is malfunctioning and thenautomatically delivers a cardioverting shock to the heart. The devicelies dormant during normal heart activity and applies a shock to theheart only when the heart functions become abnormal. This device isextremely compact and features an electrode system, in the form of anintravascular lead, which is totally and completely implantable in thebody of a patient. This single intravascular lead is used for sensingthe difference between a normally functioning heart and one which isfunctioning abnormally, and also for transmitting cardioverting shocksto the heart through the electrodes positioned on the same lead. Theintravascular lead is also capable of being used for sensing heartconditions requiring heart pacing and for transmitting pacing pulses tothe heart.

The invention features a redundant heart contraction sensing system. Twodynamic heart characteristics of the heart function-EKG and heartcontractionare monitored by the invention. A cardioverting shock istransmitted to the heart only following the elapse of a specified periodof time since the sensing of a dynamic characteristic indicative of anormally functioning heart. This aids in assuring that cardiovertingshocks will be delivered to the heart only when they are needed, andthus largely eliminates the concern over possible heart damage beingcaused by the delivery of cardioverting shocks to a properly functioningheart.

A disabling feature of the invention further guards against unnecessarycardioverting shocks being applied to the heart. A fracture in thecontraction sensor will be automatically detected by a disabling meanswhich will then disable the portion of the circuit which generates andtransmits cardioverting shocks to the heart. Therefore, a fracture inthe contraction sensor will not result in an unnecessary cardiovertingshock being applied to the heart. Further, using an endocardialimplantable electrical lead, the invention provides a reliable way ofcardioverting a malfunctioning heart with-,

out causing serious damage to the heart by the application of highenergy densities directly to the heart endocardium. The truncatedcapacitive discharge waveform used in the circuit of the invention toapply energy to the heart helps minimize the peak and total energyrequired to cardiovert the heart. Another way the invention minimizesthe energy densities applied to the heart is by applying a lower energypulse first, and then, if that pulse does not restore normal heartfunctioning, applying cardioverting pulses having higher energy content.The invention also features a counting means which automaticallydisables the cardioverting circuit after a predetermined number ofpulses have been delivered to the heart; thereby preventingcardioverting shocks from being applied when they have little chance ofrestoring the heart to normal functioning, and could damage the heart.

The invention additionally provides a means for delaying application ofthe first cardioverting pulse for a period of time, for example, toseconds, following the sensing of abnormal heart functioning. This delaygives the heart the opportunity to convert spontaneously to a normalcardiac rhythm, and also insures that cardioverting pulses are notapplied if the heart condition is not critical. There is, of course, noneed for the long built-in delay period with the succeedingcardioverting shocks as there is no longer any doubt but that the heartcondition is now critical. Accordingly, the succeeding shocks areseparated by significantly shorter time intervals.

Other features and advantages of the present invention will beset forthin, or become apparent from, the following description and claims andillustrated in the accompanying drawings, which disclose by way ofexample and not by way oflimitation, the principle of the invention andthe structural implementation of the inventive concept.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustratingbasic components of the apparatus provided by this invention;

FIG. 2 is a graph indicating the shape of electrical waves produced bythe heart during normal heartbeat action;

FIG. 3 shows electrical circuitry of the heartbeat sensing meansembodied in the apparatus of this invention;

FIG. 4 is a schematic diagram illustrating the power supply and the lowbattery indicator incorporated in the apparatus of this invention;

FIG. 5 is a schematic diagram illustrating the control meansincorporated in the apparatus of this invention;

FIG. 6 is a schematic diagram illustrating the system disabling meansincorporated in the apparatus of this invention;

FIG. 7 is a schematic diagram illustrating the regulating meansincorporated in the apparatus of this invention;

FIG. 8 is a voltage v. time diagram illustrating the voltage on theenergy storage means embodied in the inventive apparatus and the statesof the reed switch and the SCR embodied in the inventive apparatus, andhow these voltages and component states effect the wave form and voltagemagnitude of the cardioverting pulses applied to the patients heart bythe apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring generally to FIG. 1,the cardioverting apparatus of this invention includes: sensing meansshown in block 10 adapted to sense each contraction of the patientsheart; stimulation means shown in block 12 adapted to automaticallyprovide electrical impulses which can be used to cardiovert the patientsheart; an intravascular electrical lead represented in block 16 adaptedto detect heart R waves and contractions and to apply electricalimpulses to the patients heart; disabling means shown in block 14adapted to disable stimulation means [2 whenever electrical lead 16 isrendered inoperative; and a power supply for the system shown in FIG. 4.Sensing means 10 monitors heart activity and provides an electricalsignal to stimulation means 12 which corresponds with each heartcontraction. When no electrical signal is received from sensing means 10for a predetermined period of time, stimulation means 12 isautomatically activated to transmit a cardioverting electrical impulseto the heart through lead 16.

It will be understood that the normal beating of the human heartproduces electrical signals or waves which are representative of thevarious stages in the occurrenceof each heartbeat. Thus a heart beatingin sinus rhythm produces electrical waves conventionally identified asP, Q, R, S and T waves, as shown in FIG. 2. The R wave, for example, isrepresentative of a hearts ventricular contraction and can be detectedby the electrodes of a conventional electrical intravascular lead of thetype commonly used in heart pacing.

An intravascular electrical lead is diagrammatically shown as block 16in FIG. 1. This block represents an intravascular electrical lead whichis adapted to detect the EKG and contractions of the heart and to applycardioverting electrical pulses to the patients heart. In a preferredembodiment of this lead the EKG is detected using electricallyconductive electrodes; the heart contractions are detected by anelastomer body which changes impedance whenever it is flexed, as forexample, by heart contraction; and the cardioverting electrical impulsesare applied to the heart via the same electrodes as used to detect theEKG. However, it will be understood that the above-described embodimentis only one of the many different intravascular lead embodiments whichcan be advantageously used with the apparatus of this invention.

Sensing means 10 comprising EKG sensor 20, contraction sensor 22, orgate 24, and wave conformer 26 is shown in FIG. 3. Sensing means 10,using intravascular electrical lead 16, is adapted to sense R waves andheart contractions and to provide an electrical signal correspondingwith each sensed normal heartbeat.

With reference to FIG. 3, contraction sensor 22 comprises fixed resistorll4, capacitor 112, and operational amplifier 110. One side of fixedresistor 114 is connected to the 4 volt power supply. The other side ofresistor 114 is connected to the junction between electrical line 11 andto capacitor 1112 for convenience denoted as junction 113. Capacitor 112is used to AC .couple junction 113 to the input side of contractionamplifier 110. The output of amplifier is transmit ted on line 21.

Contraction sensor 22 is connected to electrical lead 16 by electricalline 11 and to or gate 24 by electrical line 21 and is adaptedto providea usable electrical signal corresponding with each heart contraction.

In a preferred embodiment, electrical line 11 is connected to aconductive elastomer body within electrical lead 16 which changesimpedance when flexed by a heart contraction. This change in impedanceis easily detectable as it will cause a change in the current flowingfrom the 4 volt power source'through resistor 114, junction 113,electrical line 11, and the elastomer body. 7

The resulting change in voltage at junction 113 is AC coupled bycapacitor 112 to operational amplifier 110 where an electrical outputsignal in the form of an electrical pulse, is generated in response tothe voltage and transmitted to the or gate 24 on electrical line 21.

EKG sensor is adapted to amplify each R wave signal detected by theelectrical lead 16 corresponding to a normal heartbeat. Morespecifically, EKG sensor 20 amplifies R waves produced by a humanheartbeat, discriminating against the electrical heart waves produced bya heart in fibrillation or otherwise abnormally functioning, as well asthe pacer pulses applied using lead 16.

EKG sensor 20 is electrically connected to electrical lead 16 viaelectrical line 13 and line 17 from stimulation means 12 and to or gate24 by electrical line 23. EKG sensor 20 comprises R wave amplifier 120,compensated monostable multivibrators 122 and 130, capacitor 124,resistor 126, and and gate 140. The input side of R wave amplifier 120and multivibrator 130 are connected to electrical line 13 at junction119. The output of multivibrator 130 is directly connected to the inputside of and gate 140, whereas the output side of amplifier 120 isconnected to the input side of and gate 140 through the seriescombination of multivibrator 122 and capacitor 124. One side of resistor126 is connected to the junction between capacitor 124 and and gate 140and the other side is connected to the system ground. The output of andgate 140 is transmitted on electrical line 23.

R wave amplifier 120 is an amplifier which operates in the same manneras those commonly used in demand pacer. It is adapted to select andamplify the R waves produced by heartbeats while discriminating againstelectrical heart waves produced by an abnormally functioning heart. Theselection of the R waves is commonly performed by amplitude andfrequency filtering.

Monostable multivibrators 122 and 130 are of a conventional design. In apreferred embodiment, the multivibrators used are conventional RCAMonostable Oscillators using COS/MOS Digital Integrated Circuits. Theexact multivibrator circuitry used in this preferred embodiment isdescribed and shown schematically in FIG. 9 of RCA Application Note'lCAN-6267.

The preferred embodiment multivibrators have two states, a high'stateand a low state. They are normally in the high state, and are switchedinto the low state, for a predetermined period of time (T,,), uponreceipt of an electrical pulse of sufficient magnitude. The period oftime (T,,) the multivibrator is in the low state and the thresholdvoltage (V of the pulse required to trigger the multivibrator into thelow state can, of course, be varied by varying the component values ofthe circuitry associated with the multivibrators. Accordingly, theoutput from the multivibrators. upon receipt ofa pulse of sufficientmagnitude (V,), will be an electrical pulse ofa predetermined pulsewidth (T Capacitor 124 and resistor 126 are electrically connectedv tomultivibrator 122 in such a way that they differentiate the output frommultivibrator 122. Thus if multivibrator 122 remains in the high state,there will be no input from multivibrator 122 through thedifferentiating circuit of capacitor 124 and resistor 126 to and" gate140. However, this differentiating circuit will provide and" gate 140with a negative spike pulse followed by a positive spike pulse at a time(T,,) later when a negative electrical pulse is generated bymultivibrator 122.

Gate 140 is a conventional and" gate. It is adapted so that it willtransmit an electrical pulse, if at the time it receives the positivepulse from the differentiating circuit of capacitor 124 and resistor126, the electrical signal received from multivibrator 130 is in a highstate. If at the time the positive spike pulse is received from thedifferentiating circuit the electrical signal received frommultivibrator 130 is in the low state, then gate 140 will not transmitan electrical pulse.

Selecting multivibrators 122 and 130 having the proper thresholdvoltages (V,) and the proper pulse widths (T will allow EKG sensor 20 todifferentiate between pacer pulses and R waves. In a preferredembodiment, multivibrator 122 will have a threshold V of 10 m-v and apulse width of T,, of 1 m-sec and multivibrator 130 will have athreshold V of 0.5 v and a pulse width of 5 m-sec. R waves from a humanheart beating in normal sinus rhythm commonly have a magnitude in the 20m-volt range when sensed through the intracardiac lead system; whereaspacer pulses are commonly in the 1.0 to 2.0 volt range. Accordingly, anormally produced R wave will be insufficient to trigger multivibrator130 into its low state but the R wave amplified by amplifier will besufficient to trigger multivibrator 122 into its low state and thus willcause the differentiating circuitry to supply a positive spike pulse togate 140 when multivibrator 122 returns to its high state 1 m-sec.later. This positive spike pulse will cause gate 140 to transmit anelectrical pulse on line 23 as multivibrator will be in the high state.Conversely, pacer pulses will trigger both multivibrator 122 andmultivibrator 130. Since the output of monostable multivibrator 122 iseffectively delayed l m-sec. by differentiation elements 124 and 126,monostable multivibrator 130 will be in the low state when gate receivesthe positive pulse from multivibrator 122. Thus gate 140 will nottransmit a pulse on line 23.

Gate 24 comprises transistors and 160. The base 151 of transistor 150 iselectrically connected to contraction sensor 22 via electrical line 21;the emitter 155 is connected directly to the system ground; and thecollector 153 is electrically connected to wave conformer 26 viaelectrical line 25. The base 161 of transistor is electrically connectedto EKG sensor 20 via electrical lead 23; the emitter is connecteddirectly to the system ground; and the collector 163 is electricallyconnected to the electrical line 25 and the collector 153 of transistor150.

Gate 24 functions as a conventional or gate. Transistors 150 and 160 arenormally in the non-conductive state; however, if an electrical pulsefrom contraction sensor 22 is received at the base 151 of transistor150, it will render transistor 150 conductive, thus providing a lowresistance electrical path from electrical line 25 to ground. Likewise,an electrical pulse from EKG sensor 20 will render transistor 150conductive; thus providing a low resistance electrical path fromelectrical line 25 to ground. Consequently, whenever an electrical pulseis received from contraction sensor 22 or EKG sensor 20 or from both,gate 24 will provide a low resistance path from electrical line 25 toground.

Wave conformer 26 is electrically connected to gate 24 via electricalline 25 and to stimulation means 12 via electrical line 15, and isadapted to conform the electrical signals received from gate 24 intopulses having substantially the same pulse width and amplitude. Theconformed electrical pulses received from wave conformer 26 have apredetermined pulse amplitude and width which is sufficient to effectthe functioning of stimulation means 12.

Wave conformer 26 comprises a programable unijunction transistor 180electrically connected in a monostable multivibrator arrangement.Programable unijunction transistor 180 has a gate input 178, an anodeinput 179, and a cathode 177. This type of transistor is commonlyreferred to as a PUT in the engineering literature. It is renderedconductive, thereby providing a low impedance from both the PUT anodeand gate to its cathode, when the anode voltage exceeds the gate voltageby a specified amount, for example, 0.7 volts.

PUT 180 is connected with its gate 178 electrically connected tojunction 181, its anode 179 electrically connected to junction 183, andits cathode 177 electrically connected to electrical line 15. Resistor194 is electrically connected between electrical line and the systemground. Junction 181the junction be tween resistors 182 and 184-iselectrically connected to gate means 24 via electrical line 25.Resistors 182 and 184 are connected in series between the 4 volt powersupply and ground, thereby forming a voltage divider which establishesthe voltage at junction 181 at a predetermined value. Junction 183 isthe junction between resistor 186 and diode 188. Resistor 186, diode 188and the parallel combination of resistors 192 and capacitor 190 areconnected between the 4 volt power supply and the system ground. Thecomponent values of resistor 186 and 192 and capacitor 190 are chosensuch that the voltage at junction 183 is kept at a predetermined valuewhich normally forces PUT 180 into a non-conducting state.

Wave conformer 26 is adapted to provide a pulse having a predeterminedamplitude and width in response to each electrical signal received fromgate 24. Whenever an electrical pulse is received by gate 24 fromcontraction sensor 22 or EKG sensor or from both, gate 24 becomesactive, providing a low resistance path from electrical line to ground.Junction 18] is electrically connected to electrical line 25 and thusbecomes connected to ground via a low resistance path whenever gate 24is active. Consequently, whenever gate 24 is active, the voltage atjunction 181 is decreased and falls to a voltage such that PUT 180 isrendered conductive.

Transistor 180 will remain conductive for a predetermined period oftime. This time period is determined by the discharge time of capacitor190.

Once PUT 180 becomes conductive, capacitor 190 is prevented fromdischarging through it by diode 188. Consequently, capacitor 190 mustdischarge through resistor 192. The capacitor 190 and resistor 192component values are selected such that capacitor 190 dis charges at apredetermined rate, thus keeping the voltage at junction 183sufficiently high to keep PUT 180 conductive for a predetermined periodof time. Accordingly, this time period establishes the pulse width ofthe pulse generated by wave conformer 26. The amplitude of the generatedpulse is established by the voltage at which junction 183 is maintainedwhile PUT 180 is conductive. The generated pulse having a predeterminedamplitude and width is transmitted to stimulation means 12 on outputline 15.

Referring to FIG. 4, the power supply. for the cardioverting system isshown schematically. With reference to FIG. 1, the system power supply(not shown) must provide the energy needed to charge storage capacitor34 as well as providing the energy needed to drive and bias thecircuitry of sensing means 10, and the associated circuitry ofstimulation means 12. This requires that it have a substantiallyconstant output, as the sensing and stimulation circuitry do notfunction well when they are driven and biased by a supply thatfluctuates significantly; that it be able to supply the relatively largeamount of energy required to charge storage capacitor 34; and that it beas compact as possible.

The above stringent requirements are met by the power supply embodimentshown in FIG. 4 which comprises a 6 volt battery 210 which drives a 4volt supply 220. The 6 volt battery 210, via a DC to DC converter 32(FIG. 1), supplies the energy needed to charge capacitor 34 (FIG. 1),whereas the 4 volt supply 220 supplies a constant driving and biasingvoltage for the circuitry of sensing means 10 and the associatedcircuitry of stimulation means 12. This particular embodiment preventsfluctuations in the output of the 6 volt battery 210, caused by thedrain put on it when the storage capacitor 34 is charged, from affectingthe 4 volt source 220 output, provided the output of the 6 volt battery210 remains above 4 volts.

A low battery indicator 230 is also shown in FIG. 4. The indicator 230is set so that it is activated whenever the power source 210 outputfalls below apredetermined voltage level, for example, 4.0 volts, and isused to drive a light emitting diode which indicates that the powersource output is below this predetermined level.

Controller 30 is shown schematically in FIG. 5. It comprises programableunijunction transistor 340, transistor 310, diode 328, capacitor 330 andresistors 326, 352, 354 and 346. Programable unijunction transistor 340has a gate input 341, an anode input 343, and a cathode 345. This typeof transistor is commonly referred to as a PUT in the engineeringliterature. It is rendered conductive, thereby providing a low impedancefrom both the PUT anode and gate to its cathode when the anode voltageexceeds the gate voltage by a specified amount, for example, 0.7 volts.Resistors 352 and 354 are electrically connected in series between the 4volt power source and the system ground. Resistor 326, diode 328, andcapacitor 330 are likewise electrically connected in series between the4 volt source and the system ground. The junction between resistors 352and 354, designated junction 335, is electrically connected to gate 341of PUT 340-the junction between resistor 326 and diode 328 designatedjunction 333, is electrically connected to anode 343 of PUT 340. Thecathode 345 of PUT 340 is electrically connected to electrical line 31and also to the system ground through resistor 346. Transistor 310 hasits collector 313 electrically connected to the junction between diode328 and capacitor 330, designated junction 320; its emitter 315electrically connected to the system ground; and its base 311electrically connected to sensing means 10 via electrical line 15.

The junction 335 voltage is maintained constant as it is the junctionbetween resistors 352 and 354 which form a voltage divider; whereas thejunction 333 volta'ge varies depending upon the charge on capacitor 330.Capacitor 330 is charged by the 4 volt energy source through the seriesconnection of resistor 326 and diode 328. In a preferred embodiment thecomponent values of capacitor 330, diode 328 and resistor 326 are chosenso that it takes approximately 5 seconds to charge capacitor 330 to thepredetermined level where it will render PUT 340 conductive. Diode 328prevents capacitor 330 from discharging through PUT 340. Sincetransistor 310 is connected across capacitor 330 to the system ground,whenever transistor 310 is rendered conductive capacitor 330 rapidlydischarges to ground. However, transistor 310 is in the nonconductivestate unless it receives an electrical signal from sensing means 10 onelectrical line 15. This signal comes from wave conformer 26 and is ofsufficient pulse amplitude and width to keep transistor 310 on longenough for capacitor 330 to totally discharge.

Consequently, whenever an electrical signal is received from sensingmeans 10, capacitor 330 will discharge, rendering PUT 340non-conductive. PUT 340 will remain non-conductive for at least seconds;longer if another pulse is received from sensing means during that fivesecond interval. However, when PUT 340 becomes conductive, it willremain conductive until a pulse is received from sensing means 10. Thisis the case since capacitor 330 cannot discharge except throughtransistor 310, and thus will remain at substantially the same voltageuntil transistor 310 is rendered conductive by a pulse from sensingmeans 10.

System disable 14, shown schematically in FIG. 6, continuously monitorsthe contraction sensing circuitry of intravascular lead 16. It isadapted and connected so that if an open circuit should occur in thecontraction sensor, whether due to a break in lead 16 or in the sensoritself, a visual alarm is activated and the controller 30 is clamped sothat it is non-conducting.

System disable 14 comprises conventional Darlington amplifier 210,visual alarm 220 in the form of a light emitting diode, and resistors230 and 240. Visual alarm 220 is electrically connected between the sixvolt power supply and input 212 of amplifier 210. Amplifier 210 iselectrically connected to the contraction sensor of intravascular lead16 at input 214 via electrical line 11. The two outputs 216 and 218 fromamplifier 210 are electrically connected to the system ground throughresistors 230 and 240 respectively. Output 216 is additionallyelectrically connected to controller 30 via electrical line 15.

When an open circuit occurs in the contraction sensing circuit, systemdisable 14 will prevent stimulation means 12 from applying acardioverting pulse to the patients heart. Specifically, when thecontraction sensing circuit is broken, the increase in voltage at input214 will render amplifier 210 conductive. Amplifier 210 will remainconductive until the break in the contraction sensing circuit isrepaired. When amplifier 210 conducts, visual alarm 220 will beactivated and an electrical signal will be transmitted to controller 30on electrical line 15. This electrical signal clamps controller 30 in anoff state thereby preventing controller 30 from activating DC-DCconverter 32 and thus prohibiting a cardioverting pulse being applied tothe patients heart.

Regulator 36 is shown schematically in FIG. 7. It controls theapplication of stimulating pulses to the heart. That is, it allowsstimulating pulses to be transmitted from capacitor 34 to the heart onlywhen they have an energy content which is sufficient so that they arelikely to be able to stimulate heart activity, but not so great so thatit is likely to cause permanent heart damage. The energy content of theapplied pulses is determined by regulator 36. Specifically, regulator 36is adapted to apply a relatively low energy cardioverting pulse first,and then if that does not restore normal heart function to apply ahigher energy cardioverting pulse.

Referring generally to FIG. 7, regulator 36 will allow energy fromcapacitor 34 to be applied to the heart when silicon controlledrectifier (SCR) 410 is in the conductive state and reed relay 420 is inthe position designated position B. If SCR 410 is in the nonconductivestate or reed switch 422 is in the position designated position A, thenenergy cannot be applied from capacitor 34 to the heart. SCR 410 andreed switch 422 (when it is in position B) are electrically connected inseries between electrical line 35 and electrical line l7electrical line17 is electrically connected to intravascular lead 16 so that it iscapable of transmitting a cardioverting pulse to the heart. Reed switch420, when it is in position A, electrically connects EKG sensor 20 tolead 16. Specifically, reed relay 420 electrically connects EKG sensor20 via electrical line 13 to lead 16 via electrical line 17.Accordingly, EKG sensor 20 is electrically disconnected from lead 16,whenever reed switch 422 is capable of transmitting energy fromcapacitor 34 to lead 16 (position B). Conversely, EKG sensor 20 iselectrically connected to lead 16 whenever reed switch 422 is incapableof transmitting energy from capacitor 34 to lead 16 (position A). Thisisolates EKG sensor 20 from the cardioverting pulse being applied to theheart.

Reed relay 420 is of conventional design. It comprises a coil 430 whichis adapted to mechanically move switch 422 from one terminal to another.Coil 430 is electrically connected at one end to 6 volt power supply andat the other to a conventional Darlington amplifier 435. When amplifier435 isactive, current flows from the 6 volt source through coil 430.This causes reed switch 422 to mechanically move from terminal A toterminal B.

SCR 410 is connected with its input 411 electrically connected toelectrical line 35; its output 413 electrically connected to terminal Bof reed switch 422; and its base 415 electrically connected to a Photo-Darlington relay 440. In a preferred embodiment relay 440 is a MonsantoMCA2 solid state relay. This relay is particularly adapted to isolateSCR 410 from the other circuit components of regulator 36. It is capableof rendering SCR 410 conductive whenever it becomes active. SCR 410 willremain conductive as long as the current path through it is notinterrupted. Specifically, SCR 410 will remain conductive, once it isrendered conductive, as long as reed switch 422 is at position B oruntil the potential on line 35 is essentially zero.

The two voltage level detectors shown generally at 460 and 480 controlSCR 410 and reed relay 420. More particularly, voltage level detector460 must be active to render SCR 410 conductive and voltage leveldetector 480 must be active to move reed switch 422 to position B.Accordingly, since SCR 410 must be conductive and switch 422 must be atposition B for energy to be transferred to the heart in the form ofcardioverting pulses, detectors 460 and 480 effectively control theapplication of the cardioverting pulses.

The elemental unit denoted level detector 480 comprises programableunijunction transistor 490, zener diode 484 and resistors 482, 486, 488and 492. Programable unijunction transistor (PUT) 490 has a gate input491, an anode input 493, and a cathode 495. PUT 490, like PUT 320 ofcontroller 30 and PUT of wave conformer 26, is rendered conductivethereby providing a low impedance from both the PUT anode and gate toits cathode when the anode voltage exceeds the gate voltage by aspecified amount, for example, 0.7 volts. Resistor 482 and zener diode484 are electrically connected in series between electrical line 35 andthe system ground. Resistors 486 and 488 are likewise electricallyconnected in series between electrical line 35 and the system ground.The junction between resistor 482 and diode 484, designated junction483, is electrically connected to the gate 491 of transistor 490-thejunction between resistor 486 and 488, designated junction 487, iselectrically connected to the anode 493 of transistor 490. The cathode495 of transistor 490 is electrically connected to Darlington amplifier435 and also to the system ground through resistor 492.

Level control 480 is voltage sensitive. It will be rendered active whenthe voltage on electrical line 35 is above some predetermined level, forexample, 550 volts and will remain active as long as the voltage of line35 remains above 550 volts. Junction 483 is held at some predeterminedvoltage, for example, 6.0 volts by zener diode 484 over a broad range ofelectrical line 35 voltages, for example, 6.0 to 1,500 volts. Resistors486 and 488 form a voltage divider, thus determining the voltage atjunction 487-the junction 487 voltage bears the same relation to theelectrical line 35 voltage as the resistive value of,resistors 486 and488. By a proper selection of the resistive values of resistors 486 and488 the voltage on electrical line 35 which is required to establish avoltage at junction 487 sufficient to render transistor 490 conductivecan be easily set at 550 volts.

Level detector 480 is electrically connected in controlling relation toreed relay 420. More particularly, the cathode 495 of transistor 490 iselectrically connected to the coil 430 of reed relay 420 throughDarlington amplifier 435. The electrical signal produced at cathode 495of transistor 490 when transistor 490 be comes conductive is transmittedto, and sufficient for activating Darlington amplifier 435. This willcause current to flow through coil 430 of reed relay 420, thus switchingreed switch 422 from terminal A to terminal B.

The element denoted level detector 460, is elementally and functionallyquite similar to that of level detector 480. Level detector 460comprises programable unijunction transistor (PUT) 470, zener diode 464,

transistor 478, and resistors 462, 466, 468, 472 and 474. PUT 470 issimilar to the PUT 490 of level detector 480. Resistor 462 and zenerdiode 464 are electrically connected in series between electrical line35 and the system ground. Resistors 466 and 468, and the par-' allelcombination of resistor 474 and transistor 478 are likewise connected inseries between electrical line 35 and the system ground. Transistor 478is connected with its collector 481 connected to the junction betweenresistors 468 and 474 and its emitter 477 connected directly to thesystem ground. The junction between resistor 462 and zener diode 464 forconvenience denoted junction 463 is electrically connected to the gate471 of PUT 470-the junction between resistors 466 and 468 forconvenience denoted junction 467 is electrically connected to the anode473 of PUT 470. The cathode475 is electrically connected to Darlingtonamplifier 445 and to the system ground through resistor 472. 3

Level control 460 is voltage sensitive. It will be rendered active whenthe voltage on electrical line 35 is above some predetermined level, forexample 900 volts. The junction 463 voltage is held at somepredetermined value, for example, 6.0 volts by zener diode 464. Avoltage of a predetermined amount, for example, 0.7 volts above thejunction 4'63 voltage is required to render PUT 470 conductive. Thejunction 467 voltage bears the same relation to the electrical line 35voltage as the resistive value of the series combination of resistor 468and the parallel combination of resistor 474 and transistor 478 bears tothe resistive value of the series combination of resistors 466, 468, andthe parallel combination of resistor 474 and transistor 47 8. Theresistive value of the parallel combination of resistor 474 andtransistor 478 will, of course, be greater when transistor 478 is in thenon-conductive state than when it is in the conductive state. Thus, theresistance of the series combination of resistor 468 and the parallelcombination of resistor 474 and transistor 478 will be larger inrelation to the resistance of the series combination of resistors 466and 468 and the parallel combination of resistor 474 and transistor 478when transistor 478 is non-conducting, than when it is conducting.Accordingly, for any given electrical line 35 voltage, the voltage atjunction 467 will be greater when transistor 478 is non-conductive thanwhen transistor 478 is conductive. The resistive values of transistors466, 468 and 474 may be selected, so that the electrical line 35 voltagerequired to render PUT 470 conductive is 700 volts when transistor 478is nonconductive, and 900 volts when transistor 478 is conductive. Thenormal state of transistor 478 is the nonconductive state.

Level control 460 is electrically connected in controlling relation toSCR 410. Specifically, cathode 475 of PUT 470 of level control 460 isconnected through Darlington amplifier 445 and Photo-Darlingtonamplifier 440 to the gate 415 of SCR 410. The electrical signal producedat cathode 475 of PUT 470 when PUT 470 is rendered conductive isamplified and processed by Darlington amplifiers 445 and 440. Theamplified and processed signal is transmitted to SCR gate 415 and iscapable of causing SCR 410 to conduct. Accordingly, SCR 410 conductswhen level detector 460 is active and level detector 460 is active whenthe voltage on electrical line 35 reaches 700 volts if transistor 478 isnon-conductive, but does not become active until the electrical line 35voltage reaches 900 volts if transistor 478 is conductive. Since reedswitch 422 will normally be in position B when the voltage on electricalline 35 is above 550 volts, whenever SCR 410 conducts, a cardiovertingpulse will be applied to the patients heart.

cathode 475 of PUT 470 is transmitted to input 591 of counter 590.Output terminal 595 is electrically connected to junction 335 ofcontroller 30 via electrical line 19. When four electrical signals havebeen received at input terminal 591 of counter 590, an electrical signalwill be provided at terminal 595 of counter 590. This electrical signalkeeps junction 335 at a voltage sufficiently high so that controller 30is disabled. Controller 30 cannot now activate DC-DC converter 32.Terminal 596 of counter 590 is connected to a reset circuit 500. When apositive electrical pulse is received at terminal 596, counter 590 willbe reset to the zero state (the state in which there is no output signalfrom counter 590).

In the preferred embodiment the counter 590 is electrically connectedvia output terminals 592, 593 and 594 to the base 479 of transistor 478in such a manner that the signal from counter 590 corresponding to eachand every electrical input signal at input terminal 591 will rendertransistor 478 conductive.

As discussed above, the conduction or nonconduction of transistor 478determines whether the cardioverting pulse applied to the heart is of a700 or a 900 voltage magnitude. Transistor 478 is nonconductive whencounter 590 is in the zero state and conductive when counter 590 is inany other state. Accordingly, the first cardioverting pulse applied tothe patients heart will have a 700 volt' magnitude, and if that does notrestore normal heart activity each succeeding pulse will have a 900 voltmagnitude.

Reset circuit 500 comprises inverters 510, 530 and 550, diode 512,resistors 514 and 526, capacitor 516, transistor 520 and nand gate 540.The inverters and the nand" gate are of conventional design. The inputof inverter 510 is electrically connected to the cathode 475 of PUT 470and the output is electrically connected to one side of diode 512. Theother side of diode 512 is electrically connected to input terminal 542of nand" gate 540. It is also electrically connected through resistor514 to the 4 volt power supply and through capacitor 516 to the systemground. Transistor 520 is connected having its base 521 electricallyconnected to electrical line 15, its emitter 525 electrically connectedto the system ground, and its collector 523 electrically connectedthrough resistor 526 to the 4 volt power source. The emitter 523 oftransistor 520 and one side of resistor 526 are electrically connectedto the input side of inverter 530. The output side of inverter 530 isconnected to input terminal 544 of nand gate 540. The output terminal546 of nand" gate 540 is electrically connected through inverter 550 toinput terminal 5960f counter 590.

Reset circuit 500 will reset counter 590 to the zero state whenever anelectrical pulse corresponding to a normal heartbeat is received fromsensing circuit 10 on electrical line 15. Circuit 500 is capable ofdifferentiating between the heart activity associated with a normalheartbeat and the activity-induced by a cardioverting pulse beingapplied to the heart. Circuit 500 is nonresponsive to the induced heartactivity, but responsive to the normal heart activity and capableofresetting counter 590 to the zero state in response thereto.

Each electrical pulse corresponding to a normal heartbeat produced bysensing circuit 10 is transmitted to the base 521 of transistor 520.This pulse causes transistor 520 to conduct which allows current to flowthrough resistor 526 and transistor 520 to the system ground as long astransistor 520 is conductive, and thus lowers the voltage at the input531 of inverter 530 for this time period. This negative pulse isinverted into a positive pulse by inverter 530 and transmitted to input544 of nand gate 540. Nand gate 540 will invert this pulse and transmitthe inverted pulse to inverter 550, provided the voltage at input 542 isnot decreased. The voltage at input 542 is decreased only when a pulseis received from an active level detector 460 which occurs only when acardioverting pulse is applied to the patients heart. Specifically, whenlevel detector 460 is active a positive pulse of short durationistransmitted to inverter 510 where it is inverted and transmitted onthrough diode 512. This negative pulse being transmitted through diode512 allows capacitor 516 to discharge thus decreasing the voltage inputat terminal 542 of and gate 540 for a period of time equal to the timerequired to recharge capacitor 516 from the 4 volt power source throughresistor 514. This period of time typically is of a long enough durationso that it keeps the voltage at terminal 542 depressed during the timein which the heart activity induced by the cardioverting pulse isexhibited.

Inverter 550 inverts the negative pulse received from gate 540 into apositive pulse which is transmitted to the input 596 of counter 590.This pulse is sufficient to reset counter 590 to the zero state. In thismanner, reset circuit 500 differentiates between a normal heart activityand the activity induced by a cardioverting pulse and resets counter 590to the zero state when the heart activity is normal.

The apparatus of this invention comprises a sensing means 10 formonitoring heart activity and a stimulation means 12 for applying ashock to the patients heart of sufficient magnitude to restore normalheart activity. The sensing means 10 controls the stimulation means 12allowing the stimulation means 12 to apply a cardioverting shock to theheart only after normal heart activity has ceased. Upon monitoring lifethreat ening arrhythmias, the apparatus of this invention automaticallycardioverts the patients heart.

As shown in FIG. 1, sensing means 10 includes EKG sensor 20, contractionsensor 22, or gate 24, and wave conformer 26. The EKG sensor 20amplifies the R wave signal detected by electrical lead 16 correspondingto normal sinus rhythm of the human heart and filters out all otherheart electrical activity. The contraction sensor 22 is responsive tothe heart contractions detected by electrical lead 16 and is adapted toprovide an electrical signal corresponding to each heart contraction.Gate 24 is constructed so that it provides an electrical output signalwhenever it receives an electrical signal from either the contractionsensor 22 or the EKG sensor 20, or both. Consequently, if either thecontraction sensor 22, relying on detected heart contraction, or the EKGsensor 20, relying on detected R waves or both provide an electricalsignal to gate 24 corresponding to a normal heartbeat, gate 24 willprovide an electrical signal in the form of a pulse corresponding to theheartbeat. Wave conformer 26 is adapted to transform these electricalpulses received from gate 24 which have varying amplitudes and widthsinto pulses having substantially the same pulse width and amplitude.Accordingly, sensing means 10 is responsive to each normal sinusheartbeatdetected by intravascular electrical lead 16 in the form of anR wave or as a heart contractionand is adapted to provide an electricalpulse having a predetermined pulse amplitude and pulse widthcorresponding with each detected heartbeat.

Stimulation means 12 is adapted to apply electrical pulses to the heartvia intravascular lead 16 for cardioverting a malfunctioning heart.These cardioverting pulses are not applied immediately upon the sensingof abnormal heart functioning, but their application is delayed for aperiod of time. This delay gives the heart the opportunity to convert tonormal heart functioning, if it is able to do so. Stimulation means 12applies a cardioverting pulse having a low energy content first, andthen, if that pulse does not restore normal heart functioning,cardioverting pulses having higher energy content will be applied untilthe heart resumes normal functioning or the cardioverter isautomatically disabled.

As shown in FIG. 1, stimulation means 12 includes controller 30, DC-DCconverter 32, capacitor 34, regulator 36, and alert system 40.Stimulation means 12 is electrically connected to sensing means 10 by anelectrical connection between wave conformer 26 of sensing means 10 andcontroller 30 of stimulation means 12 and to intravascular lead 16 viaelectrical line 17.

Controller 30 functions much like a timing device. Specifically, itprovides an electrical signal if a predetermined period of time, forexample, seconds has elapsed without an electrical signal being receivedfrom wave conformer 26. Controller 30 continues to supply an electricalsignal until it receives an electrical signal from wave conformer 26corresponding to normal heart functioning. This electrical signalactivates alert system 40 comprising both a visual and an audio alarmand activates DC--DC converter 32. Converter 32 is electricallyconnected to capacitor 34 and capable of charging capacitor 34 to a1,000 volt level.

Converter 32 is a DC-DC converter of conventional design which iscapable of increasing the power supply 33 voltage from 6 volts to 1,000volts. Voltages in the 700-1,000 volt range are necessary to chargecapacitor storage means 34 to a sufficient level so that it is capableof providing cardioverting pulses of the necessary magnitude. It takes apredetermined period of time, for example -15 seconds, to chargecapacitor means 34 to the necessary level. However, any normal heartbeatduring this interval will deactivate controller which will then disableconverter 32 and thus stop the charging cycle of energy storage means34.

Accordingly, capacitor 34 is charged to the level required forcardioverting within l5-20 seconds (five second delay in controller 30plus the 10-15 seconds needed to charge capacitor 34) following the lastsensed normal heartbeat. 7

Regulator 36--electrically connected between capacitor 34 andintravascular lead l6controls the application of energy from capacitor34 to the patients heart. It determines the energy content of theapplied pulses, allowing only pulses to be applied when they have anenergy content which is likely to be sufficient to stimulate heartactivity.

The functional operation of stimulation means 12 can be best describedwith reference to the voltage diagram of FIG. 8-a chronologicaldescription of the operation is possible using this diagram inexplaining the differences between the first pulse generated andsuceeding pulses. All times and waveforms are merely illustrative- -theactual times and waveforms depend upon the particular components andcomponent values used. FIG. 8 shows the voltage waveforms representingthe voltage on capacitor 34, the state of reed switch 422, the state ofSCR 410, and the voltage applied to the patients heart. Specifically,waveform (a) shows the voltage on capacitor 34 as represented by theelectrical line 35 voltage; waveform (b) shows the times when a voltageis applied across coil 430 of reed relay 420 as represented by thevoltage at cathode 495 of control PUT 490 in regulator 36; waveform (c)shows the times when a voltage signal is applied to gate 415 of SCR 410as represented by the voltage at cathode 475 of PUT 470 in regulator 36;and waveform (d) shows the voltage waveform of the pulse applied to thepatients heart as represented by the voltage at electrical line 17.

The active operation of stimulation means 12 begins when a pulserepresenting normal heart activity has not been received from sensingmeans 10 for 5 seconds. When this occurs controller 30 becomes activesupplying an electrical signal to converter 32. Converter 32 becomesactive and charges capacitor 34. Ittakes converter 32 approximately 9seconds to charge capacitor 34 to the 550 volt level. When capacitor 34becomes charged to the 550 volt level (line 601 in FIG. 8) PUT 490 oflevel control 480 becomes active thus switching reed relay 420 toposition B. It takes converter 32 an additional three seconds to chargecapacitor 34 to the 700 volt level. When this occurs (line 602 in FIG.8) PUT 470 of level control 460 becomes active thus rendering SCR 410conductive. With reed switch 422 in position B and SCR 410 conductive,capacitor 34 has a discharge path through the patients heart. Capacitor34 begins to discharge immediately upon SCR 410 being renderedconductive (line 602, FIG. 8) and discharges through the patients heartuntil reed switch 422 is switched to position A (line 603, FIG. '8).Reed switch 422 is switched to position A when the capacitor 34 voltageis reduced to the 500 volt level. Accord ingly, 17 seconds (5 sec. 9sec. 3 sec.) following the I last sensed normal heart activity acardioverting pulse is applied to the patients heart. This cardiovertingpulse is in a truncated capacitive discharge waveform having a peakmagnitude of 700 volts and being truncated at the 500 volt level.

If this first cardioverting pulse stimulates normal heart activity,sensing means 10 senses the resumed normal heart activity and disablesstimulation means 12-but if this first pulse did not stimulate normalheart activity, a second cardioverting pulse is needed and is suppliedby stimulation means 12. Assuming that normal heart activity has notbeen restored, controller 30 will become active again 5 secondsfollowing the first cardioverting pulse. This occurs since thecontraction sensing portion of sensing means 10 is responsive to theheart contraction caused by the cardioverting pulse. The pulse itgenerates which corresponds with the cardioverting pulse deactivatescontroller 30. It takes 5 seconds for controller 30 to be activatedagain. Capacitor 34 is still charged to nearly 500 volts 5. secondsafter the first cardioverting pulse (line 604, FIG. 8). Thus it willtake only 1 second to charge capacitor to the 550 ductive as a result ofthe first applied pulse. It takes approximately seconds to chargecapacitor 34 to the 900 volt level required to render SCR 410 conductive(line 606, FIG. 8). Once the 900 volt level is reached SCR 410 becomesconductive and capacitor 34 discharges until reed switch 422 is switchedto position A. Accordingly, I 1 seconds (5 sec. 1 sec. 5 see.) after thefirst cardioverting pulse a second cardioverting pulse also having atruncated capacitive discharge waveform is applied to the heart.

The second applied pulse has a greater energy content than the firstpulse. The energy content is greater as the peak voltage of the secondpulse (900 volts) is greater than the peak voltage of the first pulse(700 volts) and both pulses truncate at 500 volts.

If thesecond cardioverting pulse stimulates normal heart activity,sensing means 10 will sense this and disable stimulation means 12. Ifnot, a third cardioverting pulse which is similar to the second pulsewill be applied in a manner similar to that of the second pulse. If thethird pulse still does not restore normal heart functioning, stimulationmeans 12 will be disabled automatically.

Although the invention has been described with reference to a particularembodiment it will be understood that this embodiment is merelyillustrative of the applications of the principles of this invention. Itwill be further understood that numerous modifications in the inventiveembodiment may be made and other arrangements may be devised withoutdeparting from the spirit and scope of this invention.

By suitable modifications in the inventive circuitry many modificationsin the functional operation of the invention can be achieved. Forexample, a P-wave amplifier could be used instead of the describedR-wave amplifier in EKG sensor 20. A gating means which is nonresponsiveto electrical signals having a repetitive rate greater than apredetermined amount could be used in place of or in addition to or gate64 to discriminate against certain types of tachyarrhythmias and thusallow a cardioverting pulse to be applied when the heart is functioningin this manner. A dynamic heart characteristic such as heart pressurecould be monitored instead of either EKG or heart contractions.Additionally, each cardioverting pulse could have an increased energycontent; the time between cardioverting pulses could be decreased foradditional applied cardioverting pulses; or the cardioverting pulsecould be applied using an intravascular lead which is distinct from theintravascular lead which is used to sense heart activity. v

Many substitutions may, of course, be made in the circuit elements usedin the inventive circuit without materially affecting the operation ofthe invention. For example, two independent power sources could be usedinstead of having a 6 volt battery drive or 4 volt constant voltage.source; various arrangements of SCRs and/or transformers as well assolid state switching devices could be used to control the transmissionof the cardioverting pulse to the patients heart instead of theparticular arrangement of an SCR and 'a reed relay actually used; anddevices of various types could be used to perform the level detectingfunction performed by level detectors 460 and 480. Many more examplesare possible-the above-listing is anything but exhaustive.

We claim:

1. Heart contraction sensing and stimulation circuit comprising:

a. first detecting means responsive to a change in a monitoredelectrical parameter produced by the normal beating action of the heartfor providing a first identifiable electrical signal corresponding witheach heart contraction;

b. second detecting means responsive to monitored heart electricalactivity corresponding to heart contractions for providing a secondidentifiable signal corresponding with each heart contraction;

c. gating means electrically connected to receive electrical signalsfrom said first and second detecting means, said gating means forproviding an electrical output signal in response to either of saididentifiable electrical signals produced by a single heart contraction;

(1. electrical energy storage means capable of storing sufficient energyto cardiovert a malfunctioning heart;

e. electrical energy source means;

f. control means connected in controlling relation to said energystorage means and said energy source means and operatively. connected tosaid gating means and responsive thereto, said control means forcontrolling the transmission of electrical energy from said source meansto said storage means only in the absence of electrical signals fromboth the first and second detecting means for a predetermined period oftime;

g. output means adapted for connection to the heart;

h. regulating means connected in controlling relation to said energystorage means, said regulating means for permitting energy to betransmitted from said storage means to said output means when the en-'ergy stored by said storage means becomes greater than a predeterminedlevel.

2. Heart contraction sensing and stimulation apparatus comprising: 7

a. first heart monitoring means being in the form. of an elastomer bodymeans having conductive particles imbedded therein and exhibiting achange in electrical impedance upon flexing, the body means includingmeans adapted to be positioned adjacent heart muscle so that each heartcontraction causes the body means to flex thereby changing itsimpedance;

b. first detecting means responsive to a change in impedance of saidelastomer body means for providing a first identifiable electricalsignal corresponding with each heart contraction;

c. second heart monitoring means in the form of conductive electrodemeans being adapted for insertion within the human vascular system andpositioned adjacent the heart for monitoring heart electrical activityand transmitting electrical energy to the heart,

d. second detecting means responsive to the monitored heart electricalactivity corresponding to heart contractions for providing a secondidentifiable signal corresponding with each heart contraction;

e. gating means electrically connected to receive electrical signalsfrom said first and seconddetecting means, said gating means forproviding an electrical output signal in response to either of saididentifiable electrical signals produced by a single heart contraction;

f. electrical energy storage means capable of storing sufficient energyto cardiovert a malfunctioning heart;

g. electrical energy source means;

h. control means electrically connected in controlling relation to saidenergy storage means and said energy source means and operativelyconnected to said gating means and responsive thereto, said controlmeans for controlling the transmission of electrical energy from saidsource means to said storage means only in the absence of both saidfirst and second identifiable signals for a predetermined period oftime;

i. regulating. means electrically connected to said electrode means andfurther connected in controlling relation to said energy storage means,said regulating means for permitting transmission of energy from saidstorage means to said electrode means when the energy stored by saidstorage means is greater than a predetermined level; and

j. disabling means electrically connected to said first monitoring meansfor sensing a break in the electrical circuitry of said first monitoringmeans, said disabling means for preventing electrical energy from beingdelivered to said electrodes when such a break occurs.

3. The apparatus of claim 2 further comprising flexible enclosure meanssubstantially inert in living body fluids and tissue, the enclosuremeans being adapted for insertion within the vascular system of a livinganimal, the enclosure means further for enclosing, at least some of, theapparatus elements, thereby sealing them from living body fluids andtissues.

4. The apparatus of claim 2 wherein the second monitoring means includestwo conductive electrode means, one of the electrode means being adaptedto be positioned within the heart and the other electrode means beingadapted to be positioned outside the heart to monitor heart electricalactivity produced by the natural beating action of the heart.

5. The apparatus of claim 2 wherein the second detecting means includesdiscrimination means, said discrimination means for responding to theheart electrical activity produced by the natural beating action of theheart while discriminating against the heart electrical signals producedby an abnormally functioning heart and those artificially induced by aheart pacing device.

6. The apparatus of claim 2 wherein said gating means includes aconforming means, said conforming means for transforming the pulseshaving varying amplitudes and widths into pulses having substantiallythe same pulse amplitude and pulse width.

7. The apparatus of claim 2 wherein said control means has atransmitting and a non-transmitting state and includes a timing meansfor maintaining said control means in the non-transmitting state for apredetermined time interval following each signal received from saidgating means. i

8. The apparatus of claim 7 wherein the timing means includes capacitivemeans for switching said control means from the non-conductive state tothe conductive state when said capacitive means becomes charged above apredetermined level, said capacitive means being operatively connectedto said gating means so that a signal from said gating means causes thecapacitive means to discharge rendering said control meansnon-conductive.

9. The apparatus of claim 2 further comprisinga counting meansoperatively connected to said energy storage means for disabling thetransmission of electrical pulses from said energy storage means to saidelectrode means after a predetermined number of electrical pulses havebeen transmitted without an intervening heart contraction having beendetected by said first or second detecting means.

10. The apparatus of claim 2 wherein the regulating means includesmultiple level control means, said level control means being constructedand arranged such that energy will begin being transmitted from saidenergy storage means to said electrodes when the energy stored by saidstorage means is above a certain first predetermined level and willcease being transmitted when the stored energy becomes less than asecond lesser predetermined level, thereby causing the energy stored bysaid storage means to be transmitted to said electrodes in a truncatedcapacitive: discharge electrical pulse waveform.

11. The apparatus of claim 2 wherein the regulating means. includesmeans for setting the time interval between the generation of the latestpulse from said gate means and the generation of the first electricalpulse transmitted to said electrode means so that said time interval issubstantially greater than the time interval between each of thesucceeding electrical pulses transmitted to said electrodes, during thetime interval in which no pulses are provided by said gate means.

12. The apparatus of claim 2 wherein the regulating means includes meansfor increasing the energy content of all but the first electrical pulseof the series of pulses transmitted to said electrodes during the timeinterval in which there is an absence of normal heart contractions.

13. In an automatic cardioverting system comprising intravascularelectrical lead means having electrodes adapted for transmittingelectrical pulses to the heart of a living animal, sensing meansincluding electrically conductive means within said lead means andflexible therewith for sensing the action of a heart contration uponsaid lead means, means electrically connected with and responsive tosaid sensing means for continuously monitoring heart activity andproducing an identifiable electrical signal corresponding to each sensedheart contraction, and stimulation means responsive to the identifiablesignal and operatively connected to said intravascular lead forproviding cardioverting shocks to said electrodes, the improvementcomprising:

conductive means or its electrical circuitry.

1. Heart contraction sensing and stimulation circuit comprising: a.first detecting means responsive to a change in a monitored electricalparameter produced by the normal beating action of the heart forproviding a first identifiable electrical signal corresponding with eachheart contraction; b. second detecting means responsive to monitoredheart electrical activity corresponding to heart contractions forproviding a second identifiable signal corresponding with each heartcontraction; c. gating means electrically connected to receiveelectrical signals from said first and second detecting means, saidgating means for providing an electrical output signal in response toeither of said identifiable electrical signals produced by a singleheart contraction; d. electrical energy storage means capable of storingsufficient energy to cardiovert a malfunctioning heart; e. electricalenergy source means; f. control means connected in controlling relationto said energy storage means and said energy source means andoperatively connected to said gating means and responsive thereto, saidcontrol means for controlling the transmission of electrical energy fromsaid source means to said storage means only in the absence ofelectrical signals from both the first and second detecting means for apredetermined period of time; g. output means adapted for connection tothe heart; h. regulating means connected in controlling relation to saidenergy storage means, said regulating means for permitting energy to betransmitted from said storage means to said output means when the energystored by said storage means becomes greater than a predetermined level.2. Heart contraction sensing and stimulation apparatus comprising: a.first heart monitoring means being in the form of an elastomer bodymeans having conductive particles imbedded therein and exhibiting achange in electrical impedance upon flexing, the body means includingmeans adapted to be positioned adjacent heart muscle so that each heartcontraction causes the body means to flex thereby changing itsimpedance; b. first detecting means responsive to a change in impedanceof said elastomer body means for providing a first identifiableelectrical signal corresponding with each heart contraction; c. secondheart monitoring means in the form of conductive electrode means beingadapted for insertion within the human vascular system and positionedadjacent the heart for monitoring heart electrical activity andtransmitting electrical energy to the heart, d. second detecting meansresponsive to the monitored heart electrical activity corresponding toheart contractions for providing a second identifiable signalcorresponding with each heart contraction; e. gating means electricallyconnected to receive electrical signals from said first and seconddetecting means, said gating means for providing an electrical outputsignal in response to either of said identifiable electrical signalsproduced by a singlE heart contraction; f. electrical energy storagemeans capable of storing sufficient energy to cardiovert amalfunctioning heart; g. electrical energy source means; h. controlmeans electrically connected in controlling relation to said energystorage means and said energy source means and operatively connected tosaid gating means and responsive thereto, said control means forcontrolling the transmission of electrical energy from said source meansto said storage means only in the absence of both said first and secondidentifiable signals for a predetermined period of time; i. regulatingmeans electrically connected to said electrode means and furtherconnected in controlling relation to said energy storage means, saidregulating means for permitting transmission of energy from said storagemeans to said electrode means when the energy stored by said storagemeans is greater than a predetermined level; and j. disabling meanselectrically connected to said first monitoring means for sensing abreak in the electrical circuitry of said first monitoring means, saiddisabling means for preventing electrical energy from being delivered tosaid electrodes when such a break occurs.
 3. The apparatus of claim 2further comprising flexible enclosure means substantially inert inliving body fluids and tissue, the enclosure means being adapted forinsertion within the vascular system of a living animal, the enclosuremeans further for enclosing, at least some of, the apparatus elements,thereby sealing them from living body fluids and tissues.
 4. Theapparatus of claim 2 wherein the second monitoring means includes twoconductive electrode means, one of the electrode means being adapted tobe positioned within the heart and the other electrode means beingadapted to be positioned outside the heart to monitor heart electricalactivity produced by the natural beating action of the heart.
 5. Theapparatus of claim 2 wherein the second detecting means includesdiscrimination means, said discrimination means for responding to theheart electrical activity produced by the natural beating action of theheart while discriminating against the heart electrical signals producedby an abnormally functioning heart and those artificially induced by aheart pacing device.
 6. The apparatus of claim 2 wherein said gatingmeans includes a conforming means, said conforming means fortransforming the pulses having varying amplitudes and widths into pulseshaving substantially the same pulse amplitude and pulse width.
 7. Theapparatus of claim 2 wherein said control means has a transmitting and anon-transmitting state and includes a timing means for maintaining saidcontrol means in the non-transmitting state for a predetermined timeinterval following each signal received from said gating means.
 8. Theapparatus of claim 7 wherein the timing means includes capacitive meansfor switching said control means from the non-conductive state to theconductive state when said capacitive means becomes charged above apredetermined level, said capacitive means being operatively connectedto said gating means so that a signal from said gating means causes thecapacitive means to discharge rendering said control meansnon-conductive.
 9. The apparatus of claim 2 further comprising acounting means operatively connected to said energy storage means fordisabling the transmission of electrical pulses from said energy storagemeans to said electrode means after a predetermined number of electricalpulses have been transmitted without an intervening heart contractionhaving been detected by said first or second detecting means.
 10. Theapparatus of claim 2 wherein the regulating means includes multiplelevel control means, said level control means being constructed andarranged such that energy will begin being transmitted from said energystorage means to said electrodes when the energy stored by said storagemeans is above a certain first predetermined level and Will cease beingtransmitted when the stored energy becomes less than a second lesserpredetermined level, thereby causing the energy stored by said storagemeans to be transmitted to said electrodes in a truncated capacitivedischarge electrical pulse waveform.
 11. The apparatus of claim 2wherein the regulating means includes means for setting the timeinterval between the generation of the latest pulse from said gate meansand the generation of the first electrical pulse transmitted to saidelectrode means so that said time interval is substantially greater thanthe time interval between each of the succeeding electrical pulsestransmitted to said electrodes, during the time interval in which nopulses are provided by said gate means.
 12. The apparatus of claim 2wherein the regulating means includes means for increasing the energycontent of all but the first electrical pulse of the series of pulsestransmitted to said electrodes during the time interval in which thereis an absence of normal heart contractions.
 13. In an automaticcardioverting system comprising intravascular electrical lead meanshaving electrodes adapted for transmitting electrical pulses to theheart of a living animal, sensing means including electricallyconductive means within said lead means and flexible therewith forsensing the action of a heart contration upon said lead means, meanselectrically connected with and responsive to said sensing means forcontinuously monitoring heart activity and producing an identifiableelectrical signal corresponding to each sensed heart contraction, andstimulation means responsive to the identifiable signal and operativelyconnected to said intravascular lead for providing cardioverting shocksto said electrodes, the improvement comprising: disabling meanselectrically connected to said sensing means for sensing a break in saidelectrically conductive means and its electrical connection with saidmonitoring means, said disabling means for preventing cardiovertingshocks from being transmitted from said stimulating means to saidelectrode upon sensing a break in said electrically conductive means orits electrical circuitry.